Substrate holder, lithographic apparatus, device manufacturing method, and method of manufacturing a substrate holder

ABSTRACT

A substrate holder for a lithographic apparatus has a planarization layer provided on a surface thereof. The planarization layer provides a smooth surface for the formation of a thin film stack forming an electronic component. The planarization layer is of substantially uniform thickness and/or its outer surface has a peak to valley distance of less than 10 μm. The planarization layer may be formed by applying two solutions of different concentration. A surface treatment may be applied to the burls to repel a solution of the planarization layer material.

This application is a continuation of U.S. patent application Ser. No.15/131,986, filed Apr. 18, 2016, now allowed, which is a continuation ofU.S. patent application Ser. No. 13/648,069, filed Oct. 9, 2012, nowU.S. Pat. No. 9,316,927, which claims priority and benefit under 35U.S.C. § 119(e) to U.S. Provisional Patent Application No. 61/547,600,filed on Oct. 14, 2011. The entire content of each of the foregoingapplications is incorporated herein in its entirety by reference.

FIELD

The present invention relates to a substrate holder, a lithographicapparatus, a device manufacturing method, and a method of manufacturinga substrate holder.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

Lithography is widely recognized as one of the key steps in themanufacture of ICs and other devices and/or structures. However, as thedimensions of features made using lithography become smaller,lithography is becoming a more critical factor for enabling miniature ICor other devices and/or structures to be manufactured. A theoreticalestimate of the limits of pattern printing can be given by the Rayleighcriterion for resolution as shown in equation (1):

$\begin{matrix}{{CD} = {k_{1}*\frac{\lambda}{NA}}} & (1)\end{matrix}$where λ is the wavelength of the radiation used, NA is the numericalaperture of the projection system used to print the pattern, k1 is aprocess dependent adjustment factor, also called the Rayleigh constant,and CD is the feature size (or critical dimension) of the printedfeature. It follows from equation (1) that reduction of the minimumprintable size of features can be obtained in three ways: by shorteningthe exposure wavelength λ, by increasing the numerical aperture NA or bydecreasing the value of k1.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

In order to shorten the exposure wavelength and, thus, reduce theminimum printable size, it has been proposed to use an extremeultraviolet (EUV) radiation source. EUV radiation is electromagneticradiation having a wavelength within the range of 5-20 nm, for examplewithin the range of 13-14 nm. It has further been proposed that EUVradiation with a wavelength of less than 10 nm could be used, forexample within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Suchradiation is termed extreme ultraviolet radiation or soft x-rayradiation. Possible sources include, for example, a laser-producedplasma source, a discharge plasma source, or a source based onsynchrotron radiation provided by an electron storage ring.

EUV radiation may be produced using a plasma. A radiation system toproduce EUV radiation may include a laser to excite a fuel to providethe plasma, and a source collector apparatus to contain the plasma. Theplasma may be created, for example, by directing a laser beam at a fuel,such as particles of a suitable material (e.g. tin), or a stream of asuitable gas or vapor, such as Xe gas or Li vapor. The resulting plasmaemits output radiation, e.g., EUV radiation, which is collected using aradiation collector. The radiation collector may be a mirrored normalincidence radiation collector, which receives the radiation and focusesthe radiation into a beam. The source collector apparatus may include anenclosing structure or chamber arranged to provide a vacuum environmentto support the plasma. Such a radiation system is typically termed alaser produced plasma (LPP) source.

SUMMARY

In a conventional lithography apparatus, the substrate to be exposed maybe supported by a substrate holder which in turn is supported by asubstrate table. The substrate holder is often a flat rigid disccorresponding in size and shape to the substrate (although it may have adifferent size or shape). It has an array of projections, referred to asburls or pimples, projecting from at least one side. In an embodiment,the substrate holder has an array of projections on two opposite sides.In this case, when the substrate holder is placed on the substratetable, the main body of the substrate holder is held a small distanceabove the substrate table while the ends of the burls on one side of thesubstrate holder lie on the surface of the substrate table. Similarly,when the substrate rests on the top of the burls on the opposite side ofthe substrate holder, the substrate is spaced apart from the main bodyof the substrate holder. A purpose of spacing apart the substrate,substrate holder and substrate table is to reduce Van der Waals and/orelectrostatic forces which might hold the substrate down and thus reducethe force to release the substrate. An additional or alternative purposeis to help prevent a particle (e.g. a contaminating particle such as adust particle), which might be present on either the substrate table orsubstrate holder, from distorting the substrate holder or substrate.Since the total surface area of the burls is only a small fraction ofthe total area of the substrate or substrate holder, it is highlyprobable that any particle will lie between burls and its presence willhave no effect. Often, the substrate holder and substrate areaccommodated within a recess in the substrate table so that the uppersurface of the substrate is substantially coplanar with the uppersurface of the substrate table.

It is desirable to provide a thin-film electric component, e.g. one ormore electrodes, heaters and/or sensors, on the substrate holder. Anelectrode can be used, for example, for electrostatic clamping of thesubstrate. A heater and/or sensor can be used, for example, fortemperature control over a substrate area. A thin-film stack comprisingseveral components is desirable to effect multiple functions. To form areliable thin-film component, especially a thin film stack, a suitablyflat surface should be used.

A substrate holder is desirably made of a material having a lowcoefficient of thermal expansion (CTE) such as SiSiC. In order to formthe burls, material is selectively removed from a flat disc (a blank),e.g. by electric discharge machining (EDM). This process leaves asurface that is often too rough to form a reliable thin-film component;the conductive layer and/or dielectric suffers from pinholes. It hastherefore been proposed to provide a planarization layer on thesubstrate holder between the burls. The planarization layer is proposedto be a polymer layer, e.g. formed by spraying of a benzocyclobutene(BCB) solution which is then cured.

It is desirable, for example, to provide a substrate table or substrateholder on which one or more electronic components, such as one or morethin-film components, are formed.

According to an aspect of the invention, there is provided a substrateholder for use in a lithographic apparatus, the substrate holdercomprising: a main body having a surface; a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate; a planarization layer provided on at least part of the mainbody surface; and a thin film stack provided on the planarization layerand forming an electric component, the planarization layer having anouter surface having a peak to valley distance of less than about 10 μm.

According to an aspect of the invention, there is provided alithographic apparatus, comprising: a support structure configured tosupport a patterning device; a projection system arranged to project abeam patterned by the patterning device onto a substrate; and asubstrate holder arranged to hold the substrate, the substrate holderbeing as described herein.

According to an aspect of the invention, there is provided a devicemanufacturing method using a lithographic apparatus, the methodcomprising: projecting a beam patterned by a patterning device onto asubstrate while holding the substrate in a substrate holder, wherein thesubstrate holder comprises: a main body having a surface; a plurality ofburls projecting from the surface and having end surfaces to support asubstrate; a planarization layer provided on at least part of the mainbody surface; and a thin film stack provided on the planarization layerand forming an electric component, the planarization layer having anouter surface having a peak to valley distance of less than about 10 μm.

According to an aspect of the invention, there is provided a method ofmanufacturing a substrate holder for use in a lithographic apparatus,the method comprising: providing a main body having a surface and aplurality of burls projecting from the surface and having end surfacesto support a substrate; forming a planarization layer on at least partof the main body surface; and forming a thin film stack on theplanarization layer, the thin film stack forming an electric componentand the planarization layer having an outer surface having a peak tovalley distance of less than about 10 μm.

According to an aspect of the invention, there is provided a substrateholder for use in a lithographic apparatus, the substrate holdercomprising: a main body having a surface; a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate; a planarization layer provided on at least part of the mainbody surface; and a thin film stack provided on the planarization layerand forming an electric component, the planarization layer having asubstantially uniform thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a barrier member which may be used inan embodiment of the present invention as an immersion liquid supplysystem;

FIG. 6 depicts in cross-section a substrate table and a substrate holderaccording to an embodiment of the invention;

FIG. 7 is an enlarged view of a part of the substrate holder of FIG. 6;

FIG. 8 is a further enlarged view of a part of the substrate holder ofFIGS. 6 and 7;

FIGS. 9 to 14 depict steps in a method of manufacturing a substrateholder according to an embodiment of the invention;

FIGS. 15 to 18 are scanning electron microscope images of planarizationlayers on substrate holders;

FIGS. 19 to 22 depict chemical reactions in formation of a planarizationlayer in an embodiment of the invention;

FIG. 23 depicts in cross-section a substrate holder according to anembodiment of the invention;

FIG. 24 depicts in cross-section a substrate holder according to anembodiment of the invention;

FIG. 25 depicts in cross-section a substrate holder according to anembodiment of the invention;

FIG. 26 depicts steps in a method of manufacturing a substrate holderaccording to an embodiment of the invention;

FIG. 27 is a graph of Ra roughness values of planarization layers formedaccording to the method of FIG. 26 and a comparative example;

FIG. 28 is a graph of peak-valley roughness values of planarizationlayers formed according to the method of FIG. 26 and a comparativeexample;

FIG. 29 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 30 is a more detailed view of the apparatus of FIG. 29; and

FIG. 31 is a more detailed view of a source collector apparatus of theapparatus of FIGS. 29 and 30.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation, DUV radiation or EUV        radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. The supportstructure MT holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structureMT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT maybe a frame or a table, for example, which may be fixed or movable asrequired. The support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM configured to adjust theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section. Similar to the source SO, theilluminator IL may or may not be considered to form part of thelithographic apparatus. For example, the illuminator IL may be anintegral part of the lithographic apparatus or may be a separate entityfrom the lithographic apparatus. In the latter case, the lithographicapparatus may be configured to allow the illuminator IL to be mountedthereon. Optionally, the illuminator IL is detachable and may beseparately provided (for example, by the lithographic apparatusmanufacturer or another supplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

FIG. 29 schematically depicts a lithographic apparatus 1000 including asource collector apparatus SO according to an embodiment of theinvention. The apparatus comprises: an illumination system (illuminator)IL configured to condition a radiation beam B (e.g. EUV radiation); asupport structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask or a reticle) MA and connected to a firstpositioner PM configured to accurately position the patterning device; asubstrate table (e.g. a wafer table) WT constructed to hold a substrate(e.g. a resist-coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate; and a projection system(e.g. a reflective projection system) PS configured to project a patternimparted to the radiation beam B by patterning device MA onto a targetportion C (e.g. comprising one or more dies) of the substrate W. As heredepicted, the apparatus is of a reflective type (e.g. employing areflective mask).

The projection system, like the illumination system, may include varioustypes of optical components, such as refractive, reflective, magnetic,electromagnetic, electrostatic or other types of optical components, orany combination thereof, as appropriate for the exposure radiation beingused, or for other factors such as the use of a vacuum. It may bedesired to use a vacuum for EUV radiation since other gases may absorbtoo much radiation. A vacuum environment may therefore be provided tothe whole beam path with the aid of a vacuum wall and vacuum pumps.

Referring to FIG. 29, the illuminator IL receives an extreme ultraviolet radiation beam from the source collector apparatus SO. Methods toproduce EUV radiation include, but are not necessarily limited to,converting a material into a plasma state that has at least one element,e.g., xenon, lithium or tin, with one or more emission lines in the EUVrange. In one such method, often termed laser produced plasma (“LPP”)the plasma can be produced by irradiating a fuel, such as a droplet,stream or cluster of material having the required line-emitting element,with a laser beam. The source collector apparatus SO may be part of anEUV radiation system including a laser, not shown in FIG. 29, to providethe laser beam exciting the fuel. The resulting plasma emits outputradiation, e.g., EUV radiation, which is collected using a radiationcollector, disposed in the source collector apparatus.

The laser and the source collector apparatus may be separate entities,for example when a CO₂ laser is used to provide the laser beam for fuelexcitation. In such cases, the laser is not considered to form part ofthe lithographic apparatus and the radiation beam is passed from thelaser to the source collector apparatus with the aid of a beam deliverysystem comprising, for example, one or more suitable directing mirrorsand/or a beam expander. In other cases the source may be an integralpart of the source collector apparatus, for example when the source is adischarge produced plasma EUV generator, often termed as a DPP source.

The illuminator IL may comprise an adjuster to adjust the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as facetted field and pupilmirror devices. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. After being reflected from thepatterning device (e.g. mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the beam onto a target portion Cof the substrate W. With the aid of the second positioner PW andposition sensor PS2 (e.g. an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theradiation beam B. Similarly, the first positioner PM and anotherposition sensor PS1 can be used to accurately position the patterningdevice (e.g. mask) MA with respect to the path of the radiation beam B.Patterning device (e.g. mask) MA and substrate W may be aligned usingmask alignment marks M1, M2 and substrate alignment marks P1, P2.

FIG. 30 shows an embodiment of the apparatus 1000 in more detail,including the source collector apparatus SO, the illumination system IL,and the projection system PS. The source collector apparatus SO isconstructed and arranged such that a vacuum environment can bemaintained in an enclosing structure 1220 of the source collectorapparatus SO. An EUV radiation emitting plasma 1210 may be formed by adischarge produced plasma source. EUV radiation may be produced by a gasor vapor, for example Xe gas, Li vapor or Sn vapor in which the very hotplasma 1210 is created to emit radiation in the EUV range of theelectromagnetic spectrum. The very hot plasma 1210 is created by, forexample, an electrical discharge causing an at least partially ionizedplasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor orany other suitable gas or vapor may be required for efficient generationof the radiation. In an embodiment, a plasma of excited tin (Sn) isprovided to produce EUV radiation.

The radiation emitted by the hot plasma 1210 is passed from a sourcechamber 1211 into a collector chamber 1212 via an optional gas barrieror contaminant trap 1230 (in some cases also referred to as contaminantbarrier or foil trap) which is positioned in or behind an opening insource chamber 1211. The contaminant trap 1230 may include a channelstructure. Contamination trap 1230 may also include a gas barrier or acombination of a gas barrier and a channel structure. The contaminanttrap or contaminant barrier 1230 further indicated herein at leastincludes a channel structure, as known in the art.

The collector chamber 1212 may include a radiation collector CO whichmay be a so-called grazing incidence collector. Radiation collector COhas an upstream radiation collector side 1251 and a downstream radiationcollector side 1252. Radiation that traverses collector CO can bereflected off a grating spectral filter 1240 to be focused in a virtualsource point IF. The virtual source point IF is commonly referred to asthe intermediate focus, and the source collector apparatus is arrangedsuch that the intermediate focus IF is located at or near an opening1221 in the enclosing structure 1220. The virtual source point IF is animage of the radiation emitting plasma 1210.

Subsequently the radiation traverses the illumination system IL, whichmay include a facetted field mirror device 1022 and a facetted pupilmirror device 1024 arranged to provide a desired angular distribution ofthe radiation beam 1021, at the patterning device MA, as well as adesired uniformity of radiation intensity at the patterning device MA.Upon reflection of the beam of radiation 1021 at the patterning deviceMA, held by the support structure MT, a patterned beam 1026 is formedand the patterned beam 1026 is imaged by the projection system PS viareflective elements 1028, 1030 onto a substrate W held by the waferstage or substrate table WT.

More elements than shown may generally be present in illumination opticsunit IL and projection system PS. The grating spectral filter 1240 mayoptionally be present, depending upon the type of lithographicapparatus. Further, there may be more mirrors present than those shownin the Figures, for example there may be 1-6 additional reflectiveelements present in the projection system PS than shown in FIG. 30.

Collector optic CO, as illustrated in FIG. 30, is depicted as a nestedcollector with grazing incidence reflectors 1253, 1254 and 1255, just asan example of a collector (or collector mirror). The grazing incidencereflectors 1253, 1254 and 1255 are disposed axially symmetric around anoptical axis O and a collector optic CO of this type is preferably usedin combination with a discharge produced plasma source, often called aDPP source.

In an embodiment, the source collector apparatus SO may be part of anLPP radiation system as shown in FIG. 31. A laser LA is arranged todeposit laser energy into a fuel, such as xenon (Xe), tin (Sn) orlithium (Li), creating the highly ionized plasma 1210 with electrontemperatures of several 10's of eV. The energetic radiation generatedduring de-excitation and recombination of these ions is emitted from theplasma, collected by a near normal incidence collector optic CO andfocused onto the opening 1221 in the enclosing structure 1220.

The depicted apparatuses could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

In many lithographic apparatus a fluid, in particular a liquid forexample an immersion lithographic apparatus, is provided between thefinal element of the projection system using a liquid supply system IHto enable imaging of smaller features and/or increase the effective NAof the apparatus. An embodiment of the invention is described furtherbelow with reference to such an immersion apparatus, but may equally beembodied in a non-immersion apparatus. Arrangements to provide liquidbetween a final element of the projection system and the substrate canbe classed into at least two general categories. These are the bath typearrangement and the so called localized immersion system. In the bathtype arrangement substantially the whole of the substrate and optionallypart of the substrate table is submersed in a bath of liquid. The socalled localized immersion system uses a liquid supply system in whichliquid is only provided to a localized area of the substrate. In thelatter category, the space filled by liquid is smaller in plan than thetop surface of the substrate and the area filled with liquid remainssubstantially stationary relative to the projection system while thesubstrate moves underneath that area. Anther arrangement, to which anembodiment of the invention is directed, is the all wet solution inwhich the liquid is unconfined. In this arrangement substantially thewhole top surface of the substrate and all or part of the substratetable is covered in immersion liquid. The depth of the liquid coveringat least the substrate is small. The liquid may be a film, such as athin film, of liquid on the substrate.

Four different types of localized liquid supply systems are illustratedin FIGS. 2-5. Any of the liquid supply devices of FIGS. 2-5 may be usedin an unconfined system; however, sealing features are not present, arenot activated, are not as efficient as normal or are otherwiseineffective to seal liquid to only the localized area.

One of the arrangements proposed for a localized immersion system is fora liquid supply system to provide liquid on only a localized area of thesubstrate and in between the final element of the projection system andthe substrate using a liquid confinement system (the substrate generallyhas a larger surface area than the final element of the projectionsystem). One way which has been proposed to arrange for this isdisclosed in PCT patent application publication no. WO 99/49504. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletonto the substrate, desirably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet after having passed under the projection system. That is, as thesubstrate is scanned beneath the element in a −X direction, liquid issupplied at the +X side of the element and taken up at the −X side.

FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet and is taken up on the other side of the element by outletwhich is connected to a low pressure source. The arrows above thesubstrate W illustrate the direction of liquid flow, and the arrow belowthe substrate W illustrates the direction of movement of the substratetable. In the illustration of FIG. 2 the liquid is supplied along thedirection of movement of the substrate relative to the final element,though this does not need to be the case. Various orientations andnumbers of in- and out-lets positioned around the final element arepossible, one example is illustrated in FIG. 3 in which four sets of aninlet with an outlet on either side are provided in a regular patternaround the final element. Arrows in liquid supply and liquid recoverydevices indicate the direction of liquid flow.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletsand outlets can be arranged in a plate with a hole in its center andthrough which the projection beam is projected. Liquid is supplied byone groove inlet on one side of the projection system PS and removed bya plurality of discrete outlets on the other side of the projectionsystem PS, causing a flow of a thin film of liquid between theprojection system PS and the substrate W. The choice of whichcombination of inlet and outlets to use can depend on the direction ofmovement of the substrate W (the other combination of inlet and outletsbeing inactive). In the cross-sectional view of FIG. 4, arrowsillustrate the direction of liquid flow in inlets and out of outlets.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement member which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5. The liquid confinement member is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the liquid confinementand the surface of the substrate. In an embodiment, a seal is formedbetween the liquid confinement structure and the surface of thesubstrate and may be a contactless seal such as a gas seal. Such asystem is disclosed in United States patent application publication no.US 2004-0207824.

FIG. 5 schematically depicts a localized liquid supply system with afluid handling structure 12. The fluid handling structure extends alongat least a part of a boundary of the space between the final element ofthe projection system and the substrate table WT or substrate W. (Pleasenote that reference in the following text to surface of the substrate Walso refers in addition or in the alternative to a surface of thesubstrate table, unless expressly stated otherwise.) The fluid handlingstructure 12 is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). In an embodiment, aseal is formed between the barrier member and the surface of thesubstrate W and may be a contactless seal such as a fluid seal,desirably a gas seal.

The fluid handling structure 12 at least partly contains liquid in thespace 11 between a final element of the projection system PS and thesubstrate W. A contactless seal 16 to the substrate W may be formedaround the image field of the projection system so that liquid isconfined within the space between the substrate W surface and the finalelement of the projection system PS. The space is at least partly formedby the fluid handling structure 12 positioned below and surrounding thefinal element of the projection system PS. Liquid is brought into thespace below the projection system and within the fluid handlingstructure 12 by liquid inlet 13. The liquid may be removed by liquidoutlet 13. The fluid handling structure 12 may extend a little above thefinal element of the projection system. The liquid level rises above thefinal element so that a buffer of liquid is provided. In an embodiment,the fluid handling structure 12 has an inner periphery that at the upperend closely conforms to the shape of the projection system or the finalelement thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular, though this need not be the case.

In an embodiment, the liquid is contained in the space 11 by a gas seal16 which, during use, is formed between the bottom of the fluid handlingstructure 12 and the surface of the substrate W. The gas seal is formedby gas, e.g. air or synthetic air but, in an embodiment, N₂ or anotherinert gas. The gas in the gas seal is provided under pressure via inlet15 to the gap between fluid handling structure 12 and substrate W. Thegas is extracted via outlet 14. The overpressure on the gas inlet 15,vacuum level on the outlet 14 and geometry of the gap are arranged sothat there is a high-velocity gas flow 16 inwardly that confines theliquid. The force of the gas on the liquid between the fluid handlingstructure 12 and the substrate W contains the liquid in a space 11. Theinlets/outlets may be annular grooves which surround the space 11. Theannular grooves may be continuous or discontinuous. The flow of gas 16is effective to contain the liquid in the space 11. Such a system isdisclosed in United States patent application publication no. US2004-0207824.

The example of FIG. 5 is a so called localized area arrangement in whichliquid is only provided to a localized area of the top surface of thesubstrate W at any one time. Other arrangements are possible, includingfluid handling systems which make use of a single phase extractor or atwo phase extractor as disclosed, for example, in United States patentapplication publication no US 2006-0038968.

Another arrangement which is possible is one which works on a gas dragprinciple. The so-called gas drag principle has been described, forexample, in United States patent application publication nos. US2008-0212046, US 2009-0279060, and US 2009-0279062. In that system theextraction holes are arranged in a shape which desirably has a corner.The corner may be aligned with the stepping or scanning directions. Thisreduces the force on the meniscus between two openings in the surface ofthe fluid handing structure for a given speed in the step or scandirection compared to if the two outlets were aligned perpendicular tothe direction of scan.

Also disclosed in US 2008-0212046 is a gas knife positioned radiallyoutside the main liquid retrieval feature. The gas knife traps anyliquid which gets past the main liquid retrieval feature. Such a gasknife may be present in a so called gas drag principle arrangement (asdisclosed in US 2008-0212046) in a single or two phase extractorarrangement (such as disclosed in United States patent applicationpublication no. US 2009-0262318) or any other arrangement.

Many other types of liquid supply system are possible. The presentinvention is neither limited to any particular type of liquid supplysystem, nor to immersion lithography. The invention may be appliedequally in any lithography. In an EUV lithography apparatus, the beampath is substantially evacuated and immersion arrangements describedabove are not used.

A control system 500 shown in FIG. 1 controls the overall operations ofthe lithographic apparatus and in particular performs an optimizationprocess described further below. Control system 500 can be embodied as asuitably-programmed general purpose computer comprising a centralprocessing unit, volatile and non-volatile storage means, one or moreinput and output devices such as a keyboard and screen, one or morenetwork connections and one or more interfaces to the various parts ofthe lithographic apparatus. It will be appreciated that a one-to-onerelationship between controlling computer and lithographic apparatus isnot necessary. In an embodiment of the invention one computer cancontrol multiple lithographic apparatuses. In an embodiment of theinvention, multiple networked computers can be used to control onelithographic apparatus. The control system 500 may also be configured tocontrol one or more associated process devices and substrate handlingdevices in a lithocell or cluster of which the lithographic apparatusforms a part. The control system 500 can also be configured to besubordinate to a supervisory control system of a lithocell or clusterand/or an overall control system of a fab.

FIG. 6 depicts a substrate holder 100 according to an embodiment of theinvention. It is held within a recess in substrate table WT and supportssubstrate W. The main body of the substrate holder 100 a issubstantially flat and substantially corresponding in shape and size tothe substrate W, e.g., a disc. At least on a top side, in an embodimenton both sides, the substrate holder has projections 106, commonlyreferred to as burls. In an embodiment, the substrate holder is anintegral part of the substrate table and does not have burls on thelower surface. The burls are not shown to scale in FIG. 6 (or the otherFigures). In a practical embodiment, there can be many hundreds to manythousands of burls distributed across a substrate holder of diameter,e.g., 200 mm, 300 mm or 450 mm. The tips of the burls have a small area,e.g. less than 1 mm², so that the total area of all of the burls on oneside of the substrate holder 100 is less than about 10% of the totalarea of the total surface area of the substrate holder. In this way,there is a very high probability that any particle that might lie on thesurface of the substrate, substrate holder or substrate table will fallbetween burls and will not therefore result in a deformation of thesubstrate or substrate holder. The arrangement of burls can be regularor can vary as desired to provide appropriate distribution of force onthe substrate and substrate table. The burls can have any shape in planbut are commonly circular in plan. The burls can have the same shape anddimensions throughout their height but are commonly tapered. The burlscan project a distance of from about 1 μm to about 5 mm, desirably fromabout 5 μm to about 250 μm, from the rest of the surface of the mainbody of the substrate holder 100 a. The thickness of the main body 100 aof the substrate holder 100 can be in the range of about 1 mm to about50 mm, desirably in the range of about 5 mm to 20 mm

In an embodiment of the invention, the substrate holder 100 is made ofrigid material. Desirably the material has a high thermal conductivityor a low coefficient of thermal expansion. A suitable material includesSiC (silicon carbide), SiSiC (siliconised silicon carbide), Si₃N₄(silicon nitrite), quartz, and/or various other ceramic andglass-ceramics, such as Zerodur™ glass ceramic. The substrate holder 100can be manufactured by selectively removing material from a solid discof the relevant material so as to leave the projecting burls. A suitabletechnique to remove material includes electrical discharge machining(EDM), etching, machining and/or laser ablation. Some of thesetechniques leave a rough surface, e.g. having a roughness value Ra ofthe order of several microns. The minimum roughness achievable withthese removal techniques may derive from the material properties andburl manufacturing process. For example, in the case of a two-phasematerial such as SiSiC, the minimum roughness achievable is determinedby the grain size of the two-phase material. The substrate holder canalso be manufactured by growing burls through a mask. The burls are ofthe same material as the base or another suitable material and can begrown by a physical vapor deposition process or sputtering.

Such residual roughness causes difficulty in forming one or moreelectrical components, such as one or more thin film components, on thesurface of the substrate and unreliability in such components. Theseproblems may arise because the roughness causes gaps and cracks in thinlayers coated or grown on the substrate holder to form an electroniccomponent. A thin film component may have a layer thickness in the rangeof from about 2 nm to about 100 μm and may be formed by a processincluding chemical vapor deposition, physical vapor deposition (e.g.sputtering), dip coating, spin coating and/or spray coating. In anembodiment, a component formed on the substrate holder comprises a thinfilm stack, i.e. including a plurality of thin film layers. Suchcomponents are described further below.

An electronic component to be formed on the substrate table can include,for example, an electrode, a resistive heater and/or a sensor, such as astrain sensor, a magnetic sensor, a pressure sensor, a capacitive sensoror a temperature sensor. A heater and temperature sensor can be used tolocally control and/or monitor the temperature of the substrate holderand/or substrate so as to reduce undesired or induced desiredtemperature variation and stress in the substrate holder or substrate.It is desirable to control temperature and/or stress of the substrate inorder to reduce or eliminate imaging errors such as overlay errors dueto local expansion or contraction of the substrate. For example, in animmersion lithography apparatus, evaporation of residual immersionliquid (e.g. water) on the substrate may cause localized cooling andhence shrinkage of the substrate. Conversely, the energy delivered tothe substrate by the projection beam during exposure can causesignificant heating and therefore expansion of the substrate.

In an embodiment, the component to be formed is an electrode for anelectrostatic clamp. In electrostatic clamping, a potential differenceis established between the substrate, or an electrode plated on itslower surface, and an electrode provided on the substrate table and/orsubstrate holder. The two electrodes behave as a large capacitor andsubstantial clamping forces can be generated with a reasonable potentialdifference. An electrostatic arrangement can be such that a single pairof electrodes, one on the substrate table and one on the substrate,clamps together the complete stack of substrate table, substrate holderand substrate. In an arrangement, one or more electrodes may be providedon the substrate holder so that the substrate holder is clamped to thesubstrate table and the substrate separately clamped to the substrateholder.

In an embodiment, one or more localized heaters 101 are controlled bycontroller 103 to provide a desired amount of heat to the substrateholder 100 and substrate W to control the temperature of the substrateW. One or more temperature sensors 102 are connected to controller 104which monitors the temperature of the substrate holder 100 and/orsubstrate W. Arrangements using one or more heaters and temperaturesensors to locally control the temperature of a substrate are describedin co-pending U.S. patent application publication no. US 2011/0222033,which document is incorporated herein by reference in its entirety. Thearrangements described therein can be modified to make use of aresistive heater and/or temperature sensor as described herein. Voltagesource 105 generates a potential difference e.g. of the order of 10 to10,000 volts, between the substrate W and substrate holder and betweenthe substrate table WT and substrate holder and substrate table WT sothat an electrostatic force clamps the substrate W, substrate holder 100and substrate table WT together. In an embodiment, the potentialdifference is provided between an electrode on the lower surface of thesubstrate W and an electrode on the bottom of the recess in thesubstrate table WT.

FIG. 7 is an enlargement of part of the substrate holder 100 of FIG. 6showing the upper surface 107 and some burls 106 in cross-section. In anembodiment of the invention, a planarization layer 108 is provided onthe upper surface 107 in at least some areas between the burls 106. Inan embodiment the planarization layer 108 is formed in a single layer.In an embodiment, the planarization layer 108 can be provided only wherean electronic component is to be formed or across substantially theentire upper surface of the substrate holder 100. FIG. 8 shows a furtherenlargement of the planarization layer 108. As can be seen, theplanarization layer 108 fills in roughnesses of the upper surface 107and provides an upper surface 108 a that is substantially smoother thanthe surface 107. In an embodiment of the invention the roughness Ra ofthe surface 108 a is less than about 1.5 μm, desirably less than about 1μm, or desirably less than about 0.5 μm. In an embodiment, theplanarization layer 108 is formed by applying a plurality, e.g. two,layers of coating material or precursor material. Depending upon thematerial of the planarization layer 108 it can be possible to determinefrom inspection of the formed coating that it has been applied byforming multiple sub-layers. In an embodiment, the multiple sub-layersof the planarization layer 108 are formed of the same material. In anembodiment, the multiple sub-layers of the planarization layer 108 areformed of different materials. Suitable materials are discussed below.

In an embodiment, the planarization layer 108 is formed of a siliconoxide or silicon nitride-based compound with a functional group attachedto each Si atom. The functional groups can be selected from the groupconsisting of hydrogen, methyl, fluoro, vinyl and the like. In anembodiment, the planarization layer 108 is formed of Si(CH₃)₂O_(x). Inan embodiment the planarization layer 108 is formed of SiO_(x), e.g.SiO₂. In an embodiment the planarization layer 108 is formed ofbenzocyclobutene (BCB). In an embodiment the planarization layer 108 isformed of a polyimide coating material. A method of applying such amaterial is described in U.S. Pat. No. 7,524,735, which document isincorporated herein in its entirety by reference. In an embodiment theplanarization layer 108 is formed of polymer chains consisting ofSi(CH₃)₂N and Si(CH₃)₂O backbones.

The planarization layer 108 may have a thickness in the range of fromabout 0.2 μm to about 200 μm, desirably from about 2 μm to about 30 μmdetermined on a reference flat wafer. The planarization layer 108 isdesirably sufficiently thick to fill-in most or all of the roughnessesof the surface of the substrate holder. If the planarization layer 108is too thick, it is more likely to crack during curing. Applying theplanarization layer 108 in a plurality of separate coats, as describedbelow, can reduce the chance of such cracking and reduce the surfaceroughness of the final layer.

In an embodiment, the planarization layer 108 is applied by coating thesubstrate holder 100 with a polysilazane solution which is then cured toform the silicon-based planarization layer. The reaction involved isshown in FIG. 19. In an embodiment, the polysilazane solution is appliedby a spray technique. Additionally or alternatively, other techniquessuch as deep coating and spin coating can be used. FIGS. 20 to 22 depictother reactions that can be used to form a planarization layer in anembodiment of the invention. FIG. 20 depicts a reaction that proceedsvia an aqueous medium alone. FIG. 21 depicts a reaction that proceeds inan aqueous medium in the presence of heat. FIG. 22 depicts anotherreaction that proceeds in an aqueous medium in the presence of heat. Ineach of FIGS. 20 to 22, R depicts a functional group selected from thegroup consisting of hydrogen, methyl, fluoro. In an embodiment theplanarization layer 108 comprises a mixture of —Si—N— backbones from thereactant polysilazene and —Si—O— backbones from the depicted reactions.

In some circumstances, a planarization layer applied as described abovemay not provide a surface that is sufficiently smooth for reliableformation of metal or other layers to form a thin film component.Although the planarization layer described above provides improved andsufficient Ra values, if the underlying surface has high peak to valleydistances, it is likely that high peak to valley distances will bepresent in the surface of the planarization layer. The contour of theunderlying surface can be copied to the upper surface of theplanarization layer. The amplitude of peaks and valleys can be reducedbut not eliminated. A machined, uncoated SiSiC substrate often has sharppeaks of height of 40 μm or more and widths of less than 5 μm. One ormore of these sharp peaks penetrate through an underlying dielectriclayer and conductive metal layer causing an ‘electrical short’. Apartfrom these peaks, there are variations in overall flatness because ofthe surface machining process causing a contour of the SiSiC surfacewith a peak to valley distance of up to 100 μm. Such a peak-valleyprofile might not cause a pin-hole in an overlaying conductive metal andelectric layer but this profile might induce a variation in the gas gapbetween the top of the thin layer stack to the substrate for animmersion machine and a variation in the vacuum-gap between the top ofthe thin layer stack to the substrate for an EUV machine. A maximum peakto valley distance of <=10 μm is desirable. A peak to valley distance of<=0.5 μm is desirable.

Therefore, an improved method of applying a planarization layer thatreduces a peak to valley distance in the surface of the planarizationlayer is desirable. It is desirable that the material of theplanarization layer not accumulate at the burl slopes or edges. In anembodiment, the planarization layer is of substantially uniformthickness. In an embodiment the thickness of an edge region of theplanarization layer surrounding the burls is no greater than a medialregion on which the thin film stack is formed. In an embodiment, thesurface of the burls is treated to prevent accumulation thereon ofmaterial used to form the planarization layer, e.g. by application of arepellent (e.g., hydrophobic) material. FIGS. 9 to 14 illustrate stepsin an embodiment of a method of applying the planarization layer 108. Asshown in FIG. 9, a radiation-sensitive material 110, e.g. a resist, isapplied, e.g. by spin coating, across the upper surface 107 of thesubstrate holder 100. The radiation sensitive material 110 is exposedselectively to radiation and developed to expose the burls 106 as shownin FIG. 10. Next, a repellent material 111 (described further below) isapplied to form a continuous layer as shown in FIG. 11 and cured ordried. Then the remaining radiation-sensitive material 110 is removedalong with the material 111 above it so that only the burls are coatedin the material 111 as shown in FIG. 12. In another embodiment, arepellent resist is applied, exposed and developed so that it remainsonly on the burls. Then the planarization layer is applied. In anotherembodiment the material 111 is applied selectively by an inkjet printeror using a hydrophobic sticker, which may form a mushroom shape on topof the burls.

Desirably, the material 111 covers at least the entirety of each burl,including the upper flat surface and any sloped portions. However, in anembodiment there may not be a well-defined edge to the slope of theburl. In an embodiment, a part of the slope of each burl is uncovered.In an embodiment, the material 111 covers a part of the area betweenburls, but not an area where an electric component is to be formed.

Once the material 111 is applied to the desired area, the planarizationlayer 108 is applied by spraying as described above. The material thatforms the planarization layer preferentially accumulates in the area notcoated by the material 111 so that a planarization layer 108 is formedonly in the desired area. The planarization layer 108 can be applied inmultiple coating steps in order to reduce the Ra surface roughness.Optionally the material 111 is removed, as shown in FIG. 14.

In an embodiment, the repellent material is a polysilazane solution (CAG37 obtained from Clariant Advanced Materials GmbH) and the planarizationmaterial is BCB applied in an aqueous solution. Another repellentmaterial that is usable in an embodiment is octadecyltrichlorosilane(OTS). This material forms a monolayer (a layer that is a singlemolecule thick) and can be deposited by chemical vapor deposition orthrough solution. Its molecules have two ends, one hydrophilic and onehydrophobic. The hydrophilic ends are covalently bonded to a Si or SiSiCsurface and the hydrophobic organic (decyl) chain with chlorine atomsremains pointed outwards making the surface extremely hydrophobic(contact angle with water>105 degrees). Other usable repellent materialsinclude: a methyl-terminated polymer, a siloxane (e.g.polydimethylsiloxane (PDMS)), a silazane, a fluorinated material (e.g.polytetrafluoroethylene (PTFE)), a hydrophobic monolayer material and/ora silane. A hydrophobic silane monolayer can be deposited by chemicalvapor deposition with a lift-off process to remove it from selectedareas. In an embodiment, the liquidphobic material has a static contactangle to the planarization material of greater than 90°.

In an embodiment, FOTS may be used as the hydrophobic material 111. FOTSis an abbreviation of fluoro-octyl-trichloro-silane (formal name(tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane, formulaCF₃(CF₂)₅CH₂CH₂SiCl₃) which forms a self-assembled monolayer having acontact angle to water of up to or even greater than 110°. Otherflourinated silanes are also usable in an embodiment of the invention.

In an example test, to apply FOTS to burls on a test substrate holder ofSiSiC, the test substrate holder is first cleaned in an HNO₃ bath. Then,a negative resist is applied, exposed and developed so that the burlsand some test areas are free of resist and other areas are covered. Anevacuated desiccator can be used to apply a FOTS monolayer by vapordeposition. The resist may be removed using an ultrasonic bath ofacetone so that the FOTS monolayer covers only the burls.

Contact angles of static ultra-pure water droplets (measured by contactangle measuring instrument DSA30 by Kruss, Germany) in the test areasgave values in excess of 105°.

A 20 μm layer of BCB (as used above) was sprayed on to the testsubstrate holder and cured at 300° C. Inspection by confocal microscopyrevealed that the burl tops remained free of the BCB layer, as desired,and the burl profile was not undesirably changed. The FOTS monolayer wasremoved by application of a 1% aqueous solution of HF for 3 minuteswithout damage to the SiSiC burls or the BCB planarization layer.

Roughness measurements taken by scanning along 10 mm lines on theplanarization layer of the test substrate, gave Ra values of 0.67±0.3 μmand peak-valley distances of 3.35±0.8 μm, which is more than acceptablefor the desired use.

In an embodiment, a planarization material in a non-aqueous solution orformed from a non-aqueous precursor is used and the repellent materialis replaced by an attractive (e.g., hydrophilic) material. In generalterms, a surface-energy modifying agent that tends to repel the solventof the planarization material or the precursor of the planarizationmaterial is selectively applied to the substrate table. Other techniquesthan the photolithographic technique described above can be used toselectively apply the surface-energy modifying material. For example thesurface-energy modifying material can be applied by inkjet printer or bydropper.

The mechanism by which it is presently believed an embodiment of theinvention works is described below with reference to FIGS. 15 to 18.These are scanning electrode microscope (SEM) images of sample pieces ofa substrate holder. A small piece of each sample was held in a circularcavity and immersed in a transparent epoxy material. The epoxy was thencured and polished until a cross-section with two complete burls isreached. A very thin carbon layer was vapor deposited on the surface toincrease its conductivity. The surface was measured with a SEM at 10 keVe-beam. The magnifications of the images and scale bars are shown ineach image.

FIGS. 15 and 16 show a sample of a SiSiC substrate holder on which a BCBsolution was sprayed directly, without application of a hydrophobiclayer. It can be seen that the outer surface of the BCB layer is concaveand the layer varies in thickness. The BCB layer is thickest on theslopes of the burls and thinnest in a region away from the burls. BCBmaterial appears to accumulate on the slopes of the burls and in thecorners where the burls begin to rise out of the body of the substrateholder. It is believed that the accumulation of material shown reducesthe thickness of the planarization layer in the areas away from theburls as compared to an even distribution. The reduced thickness of theplanarization layer in the area where a component is to be formed allowshigh peak-to valley variation in the underlying surface to be copied tothe outer surface of the planarization layer.

FIGS. 17 and 18 show two locations of a sample on which a planarizationlayer was applied using a method according an embodiment of theinvention. Specifically, CAG 37 was applied by dropper to the burls andBCB applied by spraying. It will be seen that the resulting surface ofthe planarization layer is much flatter and there is substantially noaccumulation of material on the burl slopes or corners. In fact, theplanarization layer is thinner at its edges than in the middle.

Roughness values measured on the samples discussed above are given inTable 1 below:

Sample Ra [μm] Peak-Valley [μm] Bare SiSiC 1.8 23.3 With CAG 37 0.5 2.96With CAG 37 0.89 5.44

Ra and Peak to valley values given above where obtained using a TaylorHobson stylus profiler having a diamond tip of radius 2 μm, which isscanned over the layer to measure its profile. Ra and peak to valleydistances are obtained from the contour map. Other equivalentinstruments and methods can be used instead.

As shown in FIG. 23, an embodiment of the invention involves depositionof different layers forming a thin-film stack 200 on a (SiSiC) surfaceof a substrate holder 100 between the burls 106 in the following generalorder viz. 1) planarization layer 108, 2) isolation layer 201 (ifnecessary), 3) metal electrode lines 202 and 4) top isolation layer 203.In an embodiment of the present invention the thin layer stack 200 canbe formed on a substrate holder formed of other materials (as describedabove) or a substrate table formed of similar materials.

The planarization layer 108 is formed as described above. Theplanarization layer 108 in an embodiment has a thickness greater than 10μm measured on a reference flat substrate. Metal electrode lines 202 arepatterned on the surface of the planarization layer 108. If theplanarization layer 108 is sufficiently thick, it may also provideelectrical isolation between the substrate holder 100 (e.g., SiSiC) andthe patterned metal electrode lines 202. If desired to improveisolation, a thin layer (isolation layer) of PE CVD (Plasma EnhancedChemical Vapor Deposition) SiO_(x) can be deposited on top of theplanarization layer to provide electrical isolation between the peaks ofthe substrate holder surface and metal electrode lines if necessary. Theisolation layer 201 desirably has a thickness greater than 0.1 μm.Desirably it has a thickness less than 10 μm. In an embodiment theisolation layer 201 has a thickness of 5 μm.

Metal electrode lines 202 are deposited by photolithography or metaldeposition and etching through a hard mask. Metal electrode lines 202desirably have a width greater than 20 μm. The maximum width of themetal electrode lines is determined by their function and availablespace; it can be several 10s of millimeters. Other methods of formingthe metal electrode lines are usable. In the case of a heater and/orsensor, wide metal lines (e.g. about 1500 μm) can be used as heatingelements and narrow metal lines (e.g. about 100 μm) can be used assensor elements. For an electrostatic clamp, two halves of continuousmetal film (but isolated from the burl tops) separated by approximately500 μm from each other can be deposited to form positive and negativeelements of the electrostatic clamp. Metal electrode lines 202 desirablyhave a layer thickness greater than about 20 nm, desirably greater thanabout 40 nm. Metal electrode lines 202 desirably have a layer thicknessless than or equal to about 1 μm, desirably less than about 500 nm,desirably less than about 200 nm.

For heater and/or sensor development, patterned metal lines may consistof Ti—Pt (10 nm thick titanium for better adhesion of approximately 250nm thick platinum) lines with varying widths. Patterning of Ti/Pt can beachieved using a combination of photo resist deposition, PVD for metalfilm deposition and a lift off process. For a heater alone, widechromium lines (˜1500 μm) can be deposited by Cr film deposition (PVD)and selective Cr etching from the burl tops using a hard mask. For anelectrostatic clamp, metal electrodes can consist of aluminum, orchromium or any other conductive material and can be formed by PVD orsputtering. Alloys of these metals can also be used.

It is desirable to electrically isolate deposited metal lines from aboveand protect them from particle depositions, scratches and oxidation.Hence a top isolation layer 203 is deposited on the patternedelectrodes. For a heater or a sensor, the isolation layer can bedeposited by spray coating of BCB and/or NN 120 or SiO_(x) as describedpreviously or a combination of sprayed layers and SiO_(x). In the caseof an electrostatic clamp, a top isolation layer 203 also providesdielectric strength so that the clamping pressure and gap between thelayer stack and substrate can be tuned to desired values. In anembodiment, the top isolation layer 203 for an electrostatic clampconsists of spray coated polymer layers of BCB, NN 120 (or combinationof these two sprayed materials) or SiO_(x) alone or a combination ofsprayed polymers layers and SiO_(x), or parylene (CVD) alone. The topisolation layer 203 desirably has a layer thickness greater than about0.1 μm, desirably greater than about 1 μm. Top isolation layer 203desirably has a layer thickness less than about 10 μm, desirably lessthan about 3 μm, for a heater or sensor. For an electrostatic clamp, topisolation layer desirably has a layer thickness less than about 100 μm,desirably less than about 20 μm. In an embodiment the thickness is in arange from about 10 to about 60 μm.

Table 2 below shows examples of suitable materials per layer in order tobuild a thin film stack. Each layer may be formed of one of the listedmaterials or a combination of two or more materials.

Appl. Layer 1. Heater only 2. Sensor & Heater 3. Clamp Bottom BCB sprayBCB spray BCB spray isolation CAG 37 spray CAG 37 spray CAG 37 spray NN120 spray NN 120 spray NN 120 spray SiO_(x) SiO_(x) SiO_(x) PVD/CVD/PVD/CVD/PECVD/ PVD/CVD/PECVD/ PECVD/ Sputtering Sputtering SputteringPolyimide Spray Parylene CVD Polyimide Spray Polyimide Spray MetalChrome Platinum Chrome, layer PVD/CVD/ PVD/CVD/ Aluminum SputteringSputtering PVD/CVD/ lift-off Sputtering Top BCB spray BCB spray BCBspray isolation CAG 37 spray CAG 37 spray CAG 37 spray NN 120 spray NN120 spray NN 120 spray SiO_(x) SiO_(x) SiO_(x) PVD/CVD/ PVD/CVD/PECVD/PVD/CVD/PECVD/ PECVD/ Sputtering Sputtering Sputtering Polyimide SprayParylene CVD Polyimide Spray Polyimide Spray

Table 3 below shows examples of specific function and requirements perlayer for the applications

Appl. Layer 1. Heater only 2. Sensor & Heater 3. Clamp Planarizationreduce reduce roughness reduce roughness roughness improve flatness(pressure uniformity) Bottom moderate high electrical high dielectricisolation electrical isolation (for sensor strength isolationresolution) high volume low low temperature resistivity temperaturedifference across the low temperature difference layer difference acrossthe across the layer short response layer short response time time Metallayer heater power sensor sensitivity high voltage sensor stabilityrequirements heater power (electrode layout) Top isolation encapsulationencapsulation high dielectric strength high volume resistivity lowtemperature difference across the layer

Thin film technology offers an overlay improvement and a cost effectivesolution for heater and/or sensor development. Metal pattern designs canbe modified easily (by modifying mask designs). In an electrostaticclamp, the layer stack may avoid critical glass bonding steps used inthe current substrate clamp manufacturing process. Because the clamp canbe built up in between the burls it is possible to have SiSiC burls.This is beneficial for wear. If a platinum (Pt) metal layer is used, atitanium adherence layer can first be applied to improve adhesion of thePt layer. For an electrostatic clamp, any suitable metal having a lowresistance can be used.

Dielectric layers can be deposited by spray coating, spin coating and PECVD techniques. Spray coating is particularly suitable for depositing apolymer based layer (dissolved in organic solvent) such as a BCB and/orNN 120 layer. Sprayed layers may suffer from surface defects such aspin-holes (because of local impurities) and cracks (most likely becauseof stresses induced in the layers) if too thick layers are deposited. Itis possible to reduce the effect of these surface imperfections bycombining different deposition processes. In an embodiment of theinvention, layers can be applied using an inkjet or bubble-jet printingtechnique. This allows for local control of the layer thickness, whichcan be useful to correct for local variation in the surface contour orthe surface roughness of the substrate holder. These techniques alsoenable patterning of a conductive layer using a conductive ink. Acombination of different materials and/or layer formation techniques canbe desirable as a defect in one layer can be cured by another layer.

An embodiment of the invention is shown in FIG. 24 which is across-section of part of a substrate holder 100. This embodiment has aplanarization layer 108 which can be formed by any of theabove-described methods. Above planarization layer 108 is formed a thinfilm stack 200 comprising, in order above the planarization layer 108,first isolation layer 201, a first metal layer (e.g., metal electrodeline) 202, second isolation layer 203, a second metal layer (e.g., metalelectrode line) 204 and third isolation layer 205. Each of these layerscan be formed by a suitable method as described above. Further metallayers and further isolation layers can also be provided. In thisembodiment, the use of two or more stacked metal layers allows theformation of two or more stacked components, e.g. sensors. Stackedsensors can provide increased isolation from noise. In an embodiment,one or more metal layers can act as shielding for one or more signallines in other layers.

An embodiment of the invention is shown in FIG. 25 which is across-section of part of a substrate holder 100. This embodiment has aplanarization layer 108 which can be formed by any of theabove-described methods. Thin film stack 200 comprises first isolationlayer 201 and second isolation layer 203 sandwiching between themelectronic components 202, 206. In this way, multiple components can beformed in a single layer on the substrate. In an embodiment, each of thecomponents 202, 206 is formed by a plurality of layers, for example ofmetal-amorphous silicon-metal. In such an embodiment, one or more of thecomponents 202, 206 form a transistor or other logic device. Such logicdevices can be used to control an array of heaters disposed across thesurface of the substrate holder 100 without requiring individualconnections to each heater. The transistors can be arranged at theintersection of word and bit lines and each connected to an associatedheater to form an active matrix.

In another aspect, a further solution to the problem of accumulation ofmaterial on the slopes of burls is provided. In this aspect two layersof planarization material are applied by spraying solutions. Thesolutions used to apply the two layers have different concentrations.The method is shown in FIG. 26.

In a first step, S1 a first solution 301 of planarization material isapplied, e.g. by spraying, to substrate holder 100 in a controlledamount to achieve a first sub-layer of a desired film thickness, e.g. 20μm. In an embodiment, the first solution is a solution of BCB in theform received from the supplier (e.g., CYCLOTENE* 3022-46 AdvancedElectronics Resin supplied by The Dow Chemical Company). The firstsprayed layer is then cured S2, for example at a temperature of 200° C.for 40 mins to 1 hour. The cured layer can be activated to improveadhesion of the next layer.

In step S3 a second solution 303 of planarization material is applied,e.g. by spraying to substrate holder 100 in a controlled amount toachieve a desired film thickness, e.g. 5 μm. In applying the secondsub-layer, a different concentration of the planarization material isused. In an embodiment, the solution 301 is diluted by mixing withmesitylene solvent 302 obtained from, e.g., Sigma-Aldrich Chemi B.V. ofthe Netherlands. This solvent consists mainly of 1,3,5-trimethal benzene(C₉ H₁₂) and another equivalent can be used in its place. Afterapplication of the second sub-layer, the substrate holder is cured S4,for example at a temperature of about 250° C. or 300° C. for 1 hour.

The application of the original concentration and diluted solutions canbe performed in either order, i.e., the first sub-layer S1 may beapplied using a diluted solution and the second sub-layer may be appliedS3 using the original concentration solution. In an embodiment, theamount of diluting solvent 302 is less than about three times the weightof the original planarization material solution so that theconcentration of the solution applied to the substrate is greater thanabout 25%, compared to 100% concentration for the original solution. Inan embodiment, the amount of diluting solvent is about 1.5 times theamount of the original solution by weight leading to a concentration ofabout 40%. In an embodiment the amount of diluting solution is about 50%by weight of the original solution 301 leading to a concentration ofabout 66%. In an embodiment the amount of diluting solvent is greaterthan about 25% by weight of the original solution 301 leading to aconcentration of less than about 80% by weight.

Table 4 below shows results of experiments to demonstrate the effect ofthis embodiment. These results are also plotted in FIGS. 27 (Ra) and 28(peak to valley). Substrates A to D were coated using two layers of BCBapplied in different dilutions as indicated in Table 4. Substrate E is acomparative example on which a single layer of BCB was applied atoriginal concentration. It will be seen that the planarization layers ofsubstrates A to D have a comparable, or slightly improved, Ra valuecompared to the comparative example but also a significantly improvedpeak to valley distance.

Concentration Substrate Layer 1 Layer 2 Ra [μm] Peak-valley [μm] A 40%100% 1.08 ± 0.09 4.69 ± 0.8  B 100% 40% 0.64 ± 0.2  3.93 ± 0.99 C 66%100% 0.78 ± 0.38 3.56 ± 1.61 D 100% 66% 0.77 ± 0.2   4.1 ± 1.19 E 20 mμBCB 1.2 ± 0.2 9.2 ± 1.4 (100%)

In an embodiment, there is provided a substrate holder for use in alithographic apparatus, the substrate holder comprising: a main bodyhaving a surface; a plurality of burls projecting from the surface andhaving end surfaces to support a substrate; a planarization layerprovided on at least part of the main body surface; and a thin filmstack provided on the planarization layer and forming an electriccomponent, wherein the planarization layer has an outer surface having apeak to valley distance of less than about 10 μm.

In an embodiment, the burls have an outer surface that has been treatedto repel a solvent or precursor of the planarization layer. In anembodiment, the outer surface of the burls is treated by application ofa repellent substance. In an embodiment, the repellent substance is oneor more selected from the group consisting of: polysilazane solution;octadecyltrichlorosilane; a methyl-terminated polymer; a siloxane; asilazane; a fluorinated material; a hydrophobic monolayer material; asilane, a flourinated silane and fluoro-octyl-trichloro-silane. In anembodiment, the planarization layer comprises a first sub-layer formedon the main body and a second sub-layer formed on the first sub-layerthat have been applied by applying first and second solutions of asolvate in a solvent respectively, the first solution having a firstconcentration of the solvate and the second solution having a secondconcentration of the solvate, the first and second concentrations beingdifferent. In an embodiment, the first concentration is higher than thesecond concentration. In an embodiment, the second concentration ishigher than the first concentration. In an embodiment, the planarizationlayer is formed of a material or a combination of materials selectedfrom the group consisting of: benzocyclobutene; perhydropolysilazene,SiO2, parylene and/or polyimide. In an embodiment, the electroniccomponent is a component selected from the group consisting of: anelectrode, a heater, a sensor a transistor and a logic device. In anembodiment, the electrode is, in use, an electrode of an electrostaticclamp.

In an embodiment, there is provided a lithographic apparatus,comprising: a support structure configured to support a patterningdevice; a projection system arranged to project a beam patterned by thepatterning device onto a substrate; and a substrate holder arranged tohold the substrate, the substrate holder being according to any of thepreceding claims.

In an embodiment, the lithographic apparatus further comprises asubstrate table and wherein the substrate holder is integrated into thesubstrate table.

In an embodiment, there is provided a device manufacturing method usinga lithographic apparatus, the method comprising: projecting a beampatterned by a patterning device onto a substrate while holding thesubstrate in a substrate holder, wherein the substrate holder comprises:a main body having a surface; a plurality of burls projecting from thesurface and having end surfaces to support a substrate; a planarizationlayer provided on at least part of the main body surface; and a thinfilm stack provided on the planarization layer and forming an electriccomponent, the planarization layer having an outer surface having a peakto valley distance of less than about 10 μm.

In an embodiment, there is provided a method of manufacturing asubstrate holder for use in a lithographic apparatus, the methodcomprising: providing a main body having a surface and a plurality ofburls projecting from the surface and having end surfaces to support asubstrate; forming a planarization layer on at least part of the mainbody surface; and forming a thin film stack on the planarization layer,the thin film stack forming an electric component and the planarizationlayer having an outer surface having a peak to valley distance of lessthan about 10 μm.

In an embodiment, the method further comprises selectively treating thesurface of the burls to repel a solvent or a precursor of a materialused to form the planarization layer before forming the planarizationlayer. In an embodiment, treating the surface of the burls comprisesapplying a repellent substance to the burls. In an embodiment, applyingthe repellent substance comprises: forming a mask on the substrateholder, the mask exposing burls and shielding another part of thesubstrate holder; and applying the repellent material to the part of thesubstrate holder exposed by the mask. In an embodiment, the repellentsubstance is one or more selected from the group consisting of:polysilazane solution; octadecyltrichlorosilane; a methyl-terminatedpolymer; a siloxane; a silazane; a fluorinated material; a hydrophobicmonolayer material; a silane, a flourinated silane andfluoro-octyl-trichloro-silane. In an embodiment, a part of the surfaceof the main body underlying the thin film stack is not treated to repela solvent or precursor. In an embodiment, forming the planarizationlayer comprises: spraying a first solution of a solvate in a solventonto the substrate holder; curing the first solution to form a firstsub-layer; spraying a second solution of solvate in a solvent onto thefirst sub-layer; and curing the second solution to form a secondsub-layer, wherein the first and second solutions have differentconcentrations of the solvate. In an embodiment, the first solution hasa higher concentration of the solvate than the second solution. In anembodiment, the first solution has a lower concentration of the solvatethan the second solution. In an embodiment, the planarization layer isformed of a material or a combination of materials selected from thegroup consisting of: benzocyclobutene; perhydropolysilazene, SiO2,parylene and/or polyimide.

In an embodiment, there is provided a substrate holder for use in alithographic apparatus, the substrate holder comprising: a main bodyhaving a surface; a plurality of burls projecting from the surface andhaving end surfaces to support a substrate; a planarization layerprovided on at least part of the main body surface; and a thin filmstack provided on the planarization layer and forming an electriccomponent, the planarization layer having a substantially uniformthickness. In an embodiment, the planarization layer has an edge regionsurrounding burls and a medial region where the thin film stack isformed, the edge region having a thickness no greater than the medialregion.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications in manufacturing components with microscale, or evennanoscale features, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) and extremeultraviolet (EUV) radiation (e.g. having a wavelength of or about 365,248, 193, 157, 126, 13.5 or 6.5 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

The controllers described above may have any suitable configuration forreceiving, processing, and sending signals. For example, each controllermay include one or more processors for executing the computer programsthat include machine-readable instructions for the methods describedabove. The controllers may also include data storage medium for storingsuch computer programs, and/or hardware to receive such medium.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above, whether the immersion liquid is provided in the form ofa bath, only on a localized surface area of the substrate, or isunconfined on the substrate and/or substrate table. In an unconfinedarrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entireuncovered surface of the substrate table and/or substrate is wetted. Insuch an unconfined immersion system, the liquid supply system may notconfine the immersion liquid or it may provide a proportion of immersionliquid confinement, but not substantially complete confinement of theimmersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid inlets, one ormore gas inlets, one or more gas outlets, and/or one or more liquidoutlets that provide liquid to the space. In an embodiment, a surface ofthe space may be a portion of the substrate and/or substrate table, or asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table. The liquid supply system may optionally further includeone or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A method comprising; applying a firstsolution of a solvate of planarization material in a solvent onto anobject holder to form a first sub-layer of a planarization layer on theobject holder; and applying a second solution of the solvate ofplanarization material in a solvent onto the first sub-layer to form asecond sub-layer of the planarization layer, wherein the first andsecond solutions have different concentrations of the solvate.
 2. Themethod of claim 1, wherein the second solution has a concentration of agreater than or equal to about 25% where the first solution is treatedas having 100% concentration or wherein the first solution has aconcentration of a greater than or equal to about 25% where the secondsolution is treated as having 100% concentration.
 3. The method of claim1, wherein the second solution has a concentration of a greater than orequal to about 40% where the first solution is treated as having 100%concentration or wherein the first solution has a concentration of agreater than or equal to about 40% where the second solution is treatedas having 100% concentration.
 4. The method of claim 1, wherein thefirst sub-layer is thicker than the second sub-layer.
 5. The method ofclaim 1, wherein the second solution has a higher concentration of thesolvate than the first solution.
 6. The method of claim 1, wherein thefirst and second solutions comprise one or more selected from:benzocyclobutene; perhydropolysilazene, SiO₂, parylene and/or polyimide.7. The method of claim 1, wherein at least part of the object holder towhich the planarization layer is provided is repellent to a materialused to form the planarization layer.
 8. A substrate holder systemcomprising: a main body of a substrate holder, the main body having asurface with surface roughness; a plurality of burls projecting from thesurface and having end surfaces to support a substrate; and aplanarization layer provided on at least part of the surface of the mainbody, the planarization layer comprising at least a first sub-layer anda second sub-layer, the first-sub layer formed from a solvate ofplanarization material in a first solution and the second-sub layerformed on the first sub-layer from the solvate of planarization materialin a second solution, wherein the first and second solutions havedifferent concentrations of the solvate.
 9. The substrate holder systemof claim 8, wherein the second solution has a concentration of a greaterthan or equal to about 25% where the first solution is treated as having100% concentration or wherein the first solution has a concentration ofa greater than or equal to about 25% where the second solution istreated as having 100% concentration.
 10. The substrate holder system ofclaim 8, wherein the second solution has a concentration of a greaterthan or equal to about 40% where the first solution is treated as having100% concentration or wherein the first solution has a concentration ofa greater than or equal to about 40% where the second solution istreated as having 100% concentration.
 11. The substrate holder system ofclaim 8, wherein the first sub-layer is thicker than the secondsub-layer.
 12. The substrate holder system of claim 8, wherein thesecond solution has a higher concentration of the solvate than the firstsolution.
 13. The substrate holder system of claim 8, wherein the firstand second solutions comprise one or more selected from:benzocyclobutene; perhydropolysilazene, SiO₂, parylene and/or polyimide.14. The substrate holder system of claim 8, wherein at least part of theobject holder to which the planarization layer is provided is repellentto a material used to form the planarization layer.
 15. A methodcomprising: applying planarization material with a first concentrationonto an object holder to form a first sub-layer of a planarization layeron the object holder; applying planarization material with a secondconcentration onto the first sub-layer to form a second sub-layer of theplanarization layer; and forming an electric or electronic component onthe planarization layer, wherein the first and second concentrations aredifferent.
 16. The method of claim 15, wherein the planarizationmaterial with the second concentration has a concentration of a greaterthan or equal to about 25% where the planarization material with thefirst concentration is treated as having 100% concentration or whereinthe planarization material with the first concentration has aconcentration of a greater than or equal to about 25% where theplanarization material with the second concentration is treated ashaving 100% concentration.
 17. The method of claim 15, wherein the firstsub-layer is thicker than the second sub-layer.
 18. The method of claim15, wherein the second concentration is higher than the firstconcentration.
 19. The method of claim 15, wherein the planarizationmaterial comprise one or more selected from: benzocyclobutene;perhydropolysilazene, SiO₂, parylene and/or polyimide.
 20. The method ofclaim 15, wherein at least part of the object holder to which theplanarization layer is provided is repellent to a material used to formthe planarization layer.